1. Field of the Invention
The present invention relates generally to regenerative braking systems and methods for use in an electric vehicle, such as a battery-powered vehicle, a fuel cell vehicle, and a hybrid electric vehicle. More specifically, the present invention relates to series regenerative braking torque control systems and methods for use in an electric vehicle having brake-by-wire capability.
2. Background of the Invention
Regenerative braking techniques may be utilized by the manufacturer of an electric vehicle (EV), such as a battery-powered vehicle, a fuel cell vehicle, and a hybrid electric vehicle (HEV), as a means of increasing the overall efficiency of the electric vehicle. The basic premise of regenerative braking is to recover as much of the kinetic energy of the electric vehicle as possible during braking or slowing by operating an electric motor system as a generator system and restoring the generated electrical energy to an energy storage or battery system. This kinetic energy is otherwise dissipated as heat by a traditional hydraulic braking system.
In an electric vehicle utilizing only a hydraulic braking system, propulsion or traction functions and hydraulic braking functions are controlled by separate microcontrollers or microprocessors, including, for example, a traction controller and a brake controller. Because these functions are separated, minimum information must be shared by the microprocessors and the architectural integrity of the overall system is maintained. In an electric vehicle utilizing a regenerative braking system, however, the traction controller typically controls traction functions and regenerative braking functions. The brake controller typically controls hydraulic braking functions and regenerative braking functions. Thus, information must be shared by the microprocessors and the architectural integrity of the overall system breaks down.
Thus, what is needed are regenerative braking systems and methods which separate the traction functions, the hydraulic braking functions, and the regenerative braking functions, allocating the traction functions and the regenerative braking functions to the traction controller and the hydraulic braking functions to the brake controller. Such systems and methods would allow the amount of information which must be shared by the microprocessors to be minimized and the architectural integrity of the overall system to be maintained.
The present invention provides regenerative braking systems and methods which allocate the traction functions and the regenerative braking functions to the traction controller and the hydraulic braking functions to the brake controller. This allows the regenerative functions to be performed in a simple and elegant manner. Minimum information must be shared by the microprocessors and the architectural integrity of the overall system is maintained.
In one embodiment, a regenerative braking system for use in an electric vehicle includes an electric motor system operable for generating torque to drive and control the electric vehicle, a traction controller operable for controlling the electric motor system, a brake system operable for generating torque to drive and control the electric vehicle, and a brake controller operable for controlling the brake system. Traction functions are strictly allocated to the traction controller, braking functions are strictly allocated to the brake controller, and the brake controller is subordinated to the traction controller. The regenerative braking system also includes a communications system operable for transferring information between the traction controller and the brake controller.
In another embodiment, a regenerative braking method for use in an electric vehicle includes providing an electric motor system operable for generating torque to drive and control the electric vehicle, providing a traction controller operable for controlling the electric motor system, providing a brake system operable for generating torque to drive and control the electric vehicle, and providing a brake controller operable for controlling the brake system. Traction functions are strictly allocated to the traction controller, braking functions are strictly allocated to the brake controller, and the brake controller is subordinated to the traction controller. The regenerative braking method also includes transferring information between the traction controller and the brake controller.